1. Field of the Invention
The present invention relates to a computer system using a programmable ROM such as a flash EEPROM (Electrically Erasable and Programmable Read Only Memory) as a BIOS-ROM and, more particularly, to a computer system having a rewriting function using a rewriting floppy disk or a computer system capable of executing rewriting upon connecting a dedicated unit to a bus.
2. Description of the Related Art
A computer system such as a personal computer generally has a system ROM (Read Only Memory) for storing a BIOS (Basic Input/Output System). When the contents of this system ROM are destroyed or to be upgraded, this system ROM must be replaced with a new or corresponding one.
In recent years, a flash EEPROM (Electrically Erasable and Programmable Read Only Memory) is developed as a programmable ROM. This flash EEPROM has various advantages including one that storage data can be erased in units of blocks. For this reason, a configuration using this flash EEPROM as a system ROM to rewrite the BIOS has recently been employed.
In a system using such a flash EEPROM, to rewrite the BIOS, a BIOS rewriting utility is loaded from a floppy disk to the main memory upon bootstrap of the operating system. This system is disclosed in a U.S. Ser. No. 07/958,556 filed Oct. 8, 1992 by the same applicant.
When the flash EEPROM is used as a system ROM as described above, the BIOS can be rewritten on-board even after the shipment of a computer product. More specifically, to rewrite the BIOS held in the system ROM, the user need not open the housing of the computer unit which incorporates the BIOS-ROM nor replace a chip holding the old BIOS with a new chip. Therefore, when a flash EEPROM as a rewritable ROM is applied to the BIOS-ROM, BIOS revision can be facilitated.
A BIOS rewriting process is based on an assumption that a system such as a personal computer is normally initialized and set in a BIOS rewriting process utility execution state. The computer initialization processing, i.e., OS (Operating System) bootstrapping can be performed by executing a boot routine in the BIOS.
When the contents of the BIOS are destroyed, the operating system itself cannot be bootstrapped, and the BIOS rewriting utility cannot be executed. The BIOS contents may be destroyed by hardware faults or a power-OFF operation during the BIOS rewriting process.
Particularly, in recent years, a user can download a BIOS compatible with his own computer system or an upgraded BIOS to his own floppy disk through personal computer communication. The user can freely rewrite the BIOS using this floppy disk. In this manner, under circumstances wherein the user can freely rewrite the BIOS without using any special device, the BIOS may be destroyed during the rewriting process due to some reason such as accidental power-OFF.
When the BIOS is destroyed, it cannot be rewritten, and the contents of the BIOS cannot be repaired. In this case, the user must replace the flash EEPROM storing the BIOS with a new one storing the normal BIOS.
A trouble may also occur when a failure occurs in a boot-block program, but not in the BIOS stored in the flash EEPROM due to the following reason. The boot block of the flash EEPROM should be executed first in initializing the system. When the contents of the boot block are destroyed, various processes such as BIOS content check cannot be performed. In addition, the system cannot be bootstrapped. Therefore, when the contents stored in the flash EEPROM used as the BIOS-ROM are destroyed, the flash EEPROM itself must be replaced.